Helicopter rotor control



1. l. SIKORSKY HELICOPTER ROTOR CONTROL Aug. 1, 1950 14 Sheets-Sheet 1 Filed May 9, 1945 IGOR I. SIKORSKY INVE NTOR AGENT Aug. 1, 3.950 1. I. SIKORSKY 2,517,509

HELICOPTER ROTOR CONTROL l4 Sheets-Sheet 2 Filed May 9, 1945 IGOR I. SIKORSKY INVENTOR m mgwdm AGENT Aug. 1,1950 1. l. SIKORSKY HELICOPTER ROTOR CONTROL Filed May 9, 1945 l4 Sheets-Sheet 3 IGOR I. SIKORSKY INVENTOR AGE NT Aug. 1, 1950 v 1. l. SIKORSKY 7,5

HELICOPTER ROTOR CONTROL Filed May 9, 1945, 14 Sheets-Sheet 4 IGOR I. SIKORSKY INVENTOR g- 1950 l. I. SIKORSKY 2,517,509 A HELICOPTER ROTOR CONTROL Filed May 9, 1945 4 14 Sheets-Sheet 5 IGOR I. SIKQRSKY INVE NTOR BY/ZWG/W AGENT Aug. 1, 1950 I. I. SIKQRSKY OI 2,517,509

HELICOPTER ROTOR CONTROL Filed May 9, 1945 14 Sheets-Sheet 6 IGOR I. SIKORSKY INVENTOR wolm AGENT 1, 1950 l. 1. SIKORSKY 2,517,509

HELICOPTER ROTOR CONTRUL Filed May 9, 1945 14 Sheets-Sheet 7 IGOR I. SIKORSKY INVENTOR WdM AGENT 1, 1950 i. 1. SIKORSKY 2,517,509

HELICOPTER ROTOR CONTROL 7 Filed May 9, 1945 14 Sheets-Sheet s IGOR 'I. YSIKORSKY IQNVENTQR AGENT Aug. 1, 1950 R 1. 1. SIKORSKY 2,517,509

HELICOPTER ROTOR CONTROL Filed May 9, 1945 l4 Sheets-Sheet 9 INVENTOR AGENT IGOR I SIKORSKY Aug 1, 1950 Filed May 9, 1945 l. 1. SIKORSKY 2,517,509

HELICOPTER RUTOR CONTROL l4 Sheets-Sheet 10 82 .984 3&4 a2

Jae 366 O O aaa m :F'igdfi IGOR I. SMORSKY INVENTOR AGENT 1950 1. 1. SIKORSKY 2,517,509

HELICOPTER ROTOR CONTROL Filed May 9, 1945 14 Sheets-Sheet 11 TIP PATH PLANE? VERTICAL VI RTUAL AXIS VE RTICAL TIP PATH PLANE REAL AXIS TILTING TIP PATH PLANE OF ROTOR IGOR I. SIKORSKY INVENTOR AGENT ug- 1950 l. I. SIKORSKY 7,509

HELICOPTER ROTOR CONTROL Filed May 9, 1945 14 Sheets-Sheet 1;

TIP PATH PLANE J VIRTUAL AXIS REAL AXIS: l\aV-VERTICAL 30/ STEADY LEVEL FLIGHT Fig. 2D

LIFT

THRUST DRAG ROTOR --DRAG FUSELAGE MOMENT FUSELAGE.

( :F'g 2 [la TIP PATH PLAg DEC ELERATING IGOR 1. SIKORSKY INVENTOR OJM AGENT 1950 l. I. SIKORSKY 2,517,509

HELICOPTER ROTOR norm-" 01.

Filed May 9, 1945 14 Sheets-Sheet l3 ALNEUTRAL PLANE NORMAL TO SHAFT BLADE MOTION CYCLlC PITCH CHANGE 0 130' see 540' 72 IGOR I. SIKORSKY mvzumn wwozm AGENT 1950 l. SIKORSKY 2,517,509

HELICOPTER ROTOR CONTROL Filed May 9, 1945 l4 Sheets-Sheet 14 F CYCLIC PITCH CHANGE APPLIED BY MANUAL CONTROL.

. 24- F LAPPING CAUSED BY CYCLIC PITCH CHANGE NATURAL FLAPPING INDUCED BY ACCELERATED FOR HARD FLKIH'II) o 460 sec, 540 720 900 I REVOLUTION DEGREES 0F AZIMUTH POSITION.

/ TILT OF-TIP PATH PLANE wan-3.: 9

have To FORWARD FLIGHT.

0 V 0 I80 270 sea I :F'i Z 5' NATURAL FLAPPING AT A 20 v m aonmwn'u no CONTROL.

M FINAL FLAPPING (mo-o). 1 ,=sor cYcuc CONTROL i: APPLIED. a V FLAPPING DUE To I CONTROL DISPLACEP go o 90 I80 27 860 FROM CURVE. B.

IGOR I. SIKORSKY INVENTOR AGENT Patented Aug. 1, 1950 UNI-TED? STATES PATENT" OFFICE Claimsr (Cl. 244'17.11)

y The present invention relates to improvements in aircraft; and more particularly to animproved aircraft of the direct lift type, such as those shown in myprior patents, Nos. 2,318,259 and 2,318,260 and ordinarilyreferred to as helicopters.

In this improved structure; control mechanism is provided for improving the operation of helicopters and for rendering them more efficient. Additionally, the several component parts are constructed and arranged to eliminate disturbing effects caused by gyroscopic and transverse moblades thereof on one side of the craft will be advancinginto relatively retreating air and the blades on the other side of, the craft will beretreating with the air. The path of the air through the rotor is into the top, down through the rotor disc and back into the slip stream. Thus, the path of the air through the plane, of the rotor is directed backwardly and downwardly and has a difierent relative speed with respect to different blades at different points in their cycle of revolution. Inasmuch as th lift of a blade is a function of the square of the speed with respect to the air, the lift of the blade in the advancing portionof the cycle would be substantially in excess ofthe lift ofthe blade in a retreating portion of thecycle if the angle of incidenceof the blade remained the same.

In the present invention, the control means act upon linkages to feather, or change the pitch, of the blades cyclically during each revolution so that the tip path plane of the rotormaybe tilted with respect to the aircraft and with respect' to the earth; Thus, the controls can be operated to change the thrust line of the rotor to provide a horizontal component of thrust whichis used to propel the craft.

Gyroscopic'and transverse moments have been substantially eliminated in the present inventionahym'eans associated with the control'means mentioned above so that the blades may flap and/or feather to eliminate transient effects causedhy gusty wind or the likeso that the effect thereof 'will not upset the 1 craft.

Accordingly, it .is an object' of the invention to provide" an improved helicopterincorporating control; means: associated with r the rotor struciture forimproving the operatingcharacteristics of the craft.

It is a-further objectoi'thejinvention to provide an improved helicopter incorporating withthe rotor system a simplified control and torque counteracting mechanism for improving thestabilityof the craft.

Theaforegoing and other objects, including the details of construction and-arrangement of parts of the instant invention, willbe either obvious or'pointed out in the following specification and claims taken inview of the accompanying draw: ings; inwhich:

Fig. 1 is a plan view of the exteriorof proved helicopter.

Fig. 2is a. side elevation thereof and Fig. 3is a front elevation thereof.

Figs. 4-, 5 .and Gare views similar to Figs. 1, 2 and 3 but show the helicopter equipped with flotation gear.

r Fig; 7(isa side view of the front portion of the helicopter. with parts broken away, and parts in section to, show the construction and arrangement of parts of the control and motor. drive mecha' nisms.

Fig. 8. is a perspective view. of the gear mechanismand. cooling fan and brake and clutch mechanisni. Y

Fig, 9 is aview partly in section of the fanand clutch mechanism.

Fig. 10 is an elevational view, with parts in section, of the rotor headcontrol and drivemechanism.

Fig. 11 isa plan view ofthe rotor head.

Fig; 12 is'adi-agrammatic viewshowing the total pitchcontrol mechanism.

Fig. 13 is adiagrammatic view of the azimuthal control mechanism.

Fig. 14 is a diagrammatic View showing 'the tail rotor:drive structure andits control mechanism.

Fig-15 1s a detail sectional view of the tail rotor drive shaft suspension.

Fig. 16' is a view taken along the line lfia--I6 of Fig. 15'.

Fig. 17 is a diagrammaticview of the helicopteras itappears when in the lifting state.

Fig. 18 is a diagrammatic view showing the rotor tilted.

Fig. l -isadiagrammatic view showing the entire system in the state of accelerating.

Fig: 20 is-a diagrammatic view showing the "entiresystem under constant speed conditions;

Fi'gl zoa is aforce vector diagram.

Fig2 1 is a-diagrammatic view showing thesystem in the decelerating'condition;

Fig: 22 1s a diagram'matic view includinga chart my, im-

and small figures representing rotor position demonstrating the lifting condition.

Fig. 23 is a diagrammatic view including charts showing the action which takes place upon tilting the rotor.

Fig. 24 comprises charts showing the action of 'a rotor blade upon accelerating, and

Fig. 25 comprises charts showing the forces acting upon a rotor blade under constant speed conditions.

In describing my invention with reference to the accompanying drawings, it will be understood that all dimensions, capacities, and the like, are used illustratively only for one particular helicopter, to enable others skilled in the art to build and operate the same; and that craft of different dimensions, capacities, and the like, can be constructed by the use of present knowledge within the domain of one skilled in the aircraft arts, in view of the teachings herein presented by way of example.

Figs. 1, 2 and 3 are plan, side elevational and front elevational views respectively of a helicopter equipped for operating from land. The helicopter has a body 30 having a forward section 3! in which the seats and the controls for the craft are contained, and an empennage section 32 upon which a torque compensating tail rotor 33 is mounted. At the sides of the central portion of the body 30, triangular framework is carried for mounting landing wheels 34. A wheel carrying framework for the wheels 34 includes shock struts 35 which absorb vibrations when the craft is standing upon the ground and the mechanism is in operation, and can also damp and cushion the same when the craft alights upon the ground. A tail wheel 36 is carried by framework secured to the body 30 and is also provided with a shock strut 3'! for the same reasons. The tail wheel 36 can be placed at different positions without altering the operation of the craft. A nose skid 38 is provided to absorb shocks and prevent damage to the forward portion 3| of the craft in the event of a nose-down landing. The forward portion 3| of the helicopter 30 is provided with panels of transparent material 39 at the tops and sides, and, if desired, at the bottom, so that the pilot and passengers have a large field of vision. A door 40 shown in Fig. 2 is one of a pair mounted in similar position on opposite sides of the forward portion 3| to pr vide access to the interior of the craft.

The balance of the craft is covered by doped fabric 42 to streamline the same. The covering 42 is provided with flaps 44 that may be closed by zipper closures or buttons or the like to provide access to the interior of the rearwardly extending portion of the craft 30.

The center of gravity of the craft has been indicated by the character CG in Fig. 2 and is substantially in alignment with a hollow drive shaft 50 from an engine, not shown, to a rotor head 52. The drive shaft 50 is journaled in a pylon made up of structural members 54 (Fig. '7) that are welded to the framework of the center portion of the fuselage and arranged in a manner to be pointed out more fully hereinafter. The pylon is proportioned so that the rotor blades 56 carried by the rotor head 52 are approximately nine feet above the ground with the craft in the position shown in Fig. 2. The pylon is covered by doped fabric 58 that is faired into the covering 42 of the fuselage 30 to form a streamlined exterior for the helicopter body.

The rotor blades 56 may be constructed of fabric-covered framework, metal, plastic material, wood, or suitable combination arrangement of these or other materials. The blades 56 in the instant helicopter are made up of fabriccovered structural members carried upon metal spars 60 that have a greater diameter at the root ends, and taper to a smaller diameter at the tip ends. The spars 66 are located at 25% of the chord and carry transverse ribs of airfoil section of the type known as N. A. C. A. 0012, suitably spaced to support a fabric cover. The leading edge of the blades 56 is made of wood and weighted so that the center of gravity of a blade 56 substantially coincides with the centerline of its spar 60. A blade 56 has an area of approximately twenty-two square feet. As viewed in plan, the blades are wider at their root ends and taper toward their tip ends. As constructed and arranged with three blades spaced radially 120 degrees apart around the drive shaft 50, the total blade area is approximately sixty-six square feet. The blades are of a length so that the diameter of the disc swept by them is approximately thirtyeight feet, and the disc area is approximately 1135 square feet. The rotor blade loading is approximately thirty-five to forty pounds per square foot depending upon the load of the helicopter, assuming a normal gross weight for the entire helicopter of between 2500 and 2600 pounds.

Figs. 4, 5 and 6 show the same helicopter except that landing wheels 34 are replaced by floats 10 for rendering the craft operable upon land or water. The floats 10 are mounted upon a triangular framework 12 fastened to lugs carried by the structural parts of the center portion of the body 30. At the lower end, the framework 12 supports a pair of longitudinally extending bars 14 that receive lacings 16 which fasten to eyelets carried by flaps forming part of the floats 1B] The volume of the floats 10 is such that either one of them will displace a sufiicient amount of water to offset the weight of the entire helicopter. Thus, when both floats are in engagement with the water, they will be substantially half submerged. When the helicopter alights upon water and engages one of the floats before the other, that float can become substantially fully submerged and will exert a righting moment upon the helicopter to bring the other float into engagement with the water. In the present structure, no shock struts are needed for landing the craft upon water because the action of the float in the water will serve to damp vibrations and to bring the craft down to a gentle landing upon the surface of the water. Suitable damping means, not shown, can be incorporated in the floats H3 or in the structure mounting the floats 10 upon the body 30 to render the same stable for alighting upon solid surfaces.

In Fig. 7, the central and forward portions of the fuselage are shown with parts broken away to show the mechanism and structure of the inside of the craft. The framing is built up of heavy tubing in the center portion (parts of which are shown) shaping the outside of the craft. Tubes extend inwardly and downwardly from the top truss members and 82 to support the gear mechanism contained in a housing 84. The structural members 54 shaping the pylon extend upwardly from the members 80 and 82. Truss rods 86 and 88 extend forwardly and connect to a heavy vertical bar 90 at its ends. Lighter frame members are used to form the forward section 3! of the body, and lighter members also extend rearwardly to support the empennage structure .32. The iframework icarrying the landing wheels 34 [is ,securedto .I lugs .carried by the heavy icenteryframing member.

The gear reduction mechanism; 84 aIEig. ,8) :may be of :anysuitable I type, and pin the instant 1 device provides agear .ratio1of 9.336/1 for-driving the rotor shaft 50. Ajhigher :speed portion ofthe gear reduction mechanism turns .aazshaft 94 ,con- I nected by a universal joint 1961.110 the taillrotor drive shaft I08. ,Power enters the reduction gearing 84 through the shaft {I06 driven by a shaft H32 through universal joints [.04. An .oil sump I08 is formed as aa'portion .of the casing for the gear mechanism 84 and is equipped with fins for cooling the oil. .Anoil-tank IJll QFig- 7.) which has a filling and air vent H2 is mounted upon ,a platform ,I' I4 carried by :adjacent .s'truc tural members of the fuselage. .Aifuel tank :6 is mounted upon. the ,lower framing members 1 for thebody of the fuselage. I

Cooling air for the engine L92 lsrdrawn into the interior of the fuselage 130throughan opening in theforward portion of thepylonfi'l (Fig.7). The air travels downwardly and around the gear reduction mechanism andis drawn through the engine by a fan I22 mounted on the drive shaft of the engine (Figs. '7 and 3).. The ain afterpass ing the engine, isdirectededownwardly or tosthe sides, by a firewall I24 which forms :a partition between the center portionIof the fuselage of the body 3!] and the forward, :occupantsuportion 22. Thereafter, the air may pass out of the fuselage through holes, notshown. The fan 122 is of the axial flow type having vanes 123.

, An electric engine starter I (Fig. .8) is provided. A safety device is also provided sothat the engine cannot be started when the clutch, to be described hereinafter, connecting the engine with the rotor gear mechanism 184, is engaged. The safety device comprises an eleotricalswlitch 135 connected bya cable :I 38 toztherstarter motor I30 Switch I36 has a lever :I 40 arranged for operation by the clutch-and-brake lever I42 pivoted at I48 and used by the operator to engagearotor brake I44 for stopping therotor and for engaging the clutch I46 for driving the rotor. When theilever M2 is moved :to the right as viewed in Fig. Emit will cause. a link I50 to be moved toward the right to rock a yoke I52 around apivot I54 to move a collar I55 to engage xtheclutch I 4.6 in a manner to be .hereinaftermore fully described. At the same time, a 108.1316. 1I'58::will be slacked off to permit a lever I to be moved :by the tension of a spring I62 to releasea brake band in a brake mechanism I54 so that the brake is therefore released and the rotor drive shaft 50 may be turned. The arm I42. also has a neutral position in which the brake. I64 is released and thecliitch M6 is not engaged. The switch lever I40 engages the arm I42 so that the starter I30 can be operated only when the clutch 146 is disengaged.

Fig. 9 shows a portion of the engine 92 and a section of the fan I22 and the clutch mochanism I45. Yoke lever il52=pivotedat I54can move $001121 I56 backand forth along the shaft of-the engine 92. The collar I56 is secured to one race [65 of a ball bearing and holds the same non rotatablyt Another race 4680f the ball bearing is free to turn, and engages, levers I'IIl carried by lugs IFIZ on the hub #126 of the fan 422. When collar I56 1:; moved toward the right, a series of clutch surfaces 182 of. a clutchtplate 4184 con- :nected to a .bell 186 :of the' rclutch aoiitputlsidea The bell I86 :drives a conventional zzfree-iwheel device IBI, which in turn .Ldi'iVS :the universal joint I04 through shaft I'IIL 'llhu's,awh-en the lever I59 is moved toward the :leftas viewed in Figsu8iand 9, the .clutch surfaces I82 willsbetdis engaged. wWhen rod IBDis moved towards the right, the springs H8 will i301] .upon 'thelplate M6 to cause ithe clutch surfaces I82 to engage and the engine 92 will turn thebell 186 011 the clutch output side.

.zReferringxagain to Fig. 'l, .thel f'or-ward portion 311 rof the body 138 contains two side by-side seats I for the 'lpilot and a passenger. :An occupant of "either seat can reach the clutch and brake lever :I it, axtotalzpitch lever iI SZ'landianaZimuthaI controlzstick, :or joy stick, 1594, for controlling the direction of flight .ofthe aircraft. Pedals I186 are arranged so that Ian occupant "of either seat lflllvlcan operate them withihis feet .(Eigsll. The pedals IiQIl rotate upon pivots I 98 to move a lever arm .499 to aposition a cable 200 leading through properly arranged pulleys to the :tail *rotorhom tro'l :to be described more fully hereinafter. instrument panel 2&2 .may contain motor speed indicators, rotor speed indicators, air speed il'ldie caters, yroscopic equipment, ignition rtmtrul's athrottle, and other .similar equipment found in mostlaircraft.

The total pitch :lever ltiiturnsupcn apivot mlt secured to the frame and moves a series of rods and bell cranks 295,208, 2H], '21 Za'ndB I4to rock a link Ett pivoted at 2H5 on the housing of reduction gear mechanism '84. Through this linkage, when the lever M2, is moved, a rod 2 2-0 helicopter in response to the position 0f the joy stick 1%.

Figs. 10 and ill, the details b'f-construction of the .rotor mechanism :52 are shown. Thestruc turalzmemberssfi l of the pylon are welded to a downwardly flared ring 23!] forming a support for a cup 232.. The cup 2:32 containsinner and outer ball :rac'es 234 and 235, thei1inerra'ce retracing secured. :to the drive shaft 59 and the outermce 2136 being :fitted to the interior of the cup Secured by locl'z nut238at the-topof shafti b upon splines 236a is a hub 2M which mountsflapping links 2&2 for turning the rotor blade's' li fi. An upper extension 2'44 of the shaft -50 carries brackets zilit. which turn with the shaft 59'. The brackets I246 are formed of triangular memberssecured together at their tops b ya plate 248 carrying pairs oftlugs 250 and also secured together at: their vertical edges by an axial tube wh ich ha's aspli'nedconnection to shaft extension 244 per-- mitting the brackets to bemoved' vertically asa unit-by rod 228. The latter is connected to the bracket connecting plate 2'4'8 at its upper end.

Rocker links-252 are carried-by 'piirotsififi in the lugs 25%. The links 252 have pivots 256st their outer ends engagedby uhiversalco'nnections 258; of 110518 250 which halve ball universal joints 2:62? at their lower ends @onn'ted to th "extremities" 7 of.:arms 264 ofa'three-pointed star 266. The ball joints 262 are protected from dirt and weather by flexible boots 268.

The star 266 is mounted upon the drive shaft 50 by a gimbal joint 210 so that when the shaft 50 is rotated, the star 266 rotates with it and is free to tilt about the pivots of the girnbal joint 210' in any direction. The star 266 carries upon a ball race 272 a pair of control arms 274 for controlling the angle of the star which arms are connected, respectively, to theupper ends of control rods 226 and 228. Arm 224 which is connected to control rod 226 is directed aft, While arm 214 which is connected to control rod 228 is directed laterally. The arms 214 are maintained non-rotatably with respect to the pylon of the helicopter body by a flexible linkage 276 comprising a knee joint made up of pivoted arms 21B and 280 swivelly connected at 232 to one arm 214 at one end and non-rotatably pivoted at the other end upon a pin 284 carried by lugs 286 bolted to the cup 232 and ring 230. By such an arrangement, the control arm 214 can be moved up and down and swivel freely upon the swivel joint 262 but the arms 274 cannot rotate with respect to the pylon. Thus, the star 266 will rotate with the shaft and carry'the arm 260 with the shaft, the rocker arm 252 will be rotated by the upper part 244 of the shaft, and all of these parts will rotate at the same speed. The control arms 274, however, which connect to the stationary controls of the helicopter are held non-rotatably and the ball bearings 272 permit movement between the star 266 and the arms 214. At the outer extremities of the arms 214, the control arms 226 and 228 are mounted by ball joints 290. The ball joints are protected from dirt and from the weather by boots 292.

The flapping links 242 are mounted upon horizontal pins 294 secured to lugs 296 extending upwardly from the hub 246. The centerlines of the pivots 294 intersect the centerline of the shaft 50. With such structure, the flapping links 242 can move upwardly to permit the rotor blades 56 to assume a COIliIlg angle and to flap as they rotate. Vertical pins 290 have their centerlines at ninety degrees to the centerline of the pivots 294 and mount an internal shank 300 for the rotor blade stub shafts 302. The rotor blades 56 can move backwardly and forwardly about the pivots 298 in an action known as hunting, which action is restrained by dampers to be described hereinafter.

The stub shafts 302 are mounted upon bearings for rotating about the shanks 360. The bearing mounts have been shown partly in section in the upper right hand part of Fig. 11 and are arranged in compression in the inside of the stub shafts 302 to resist centrifugal forces and prevent the same-from slipping off the shanks 300 while permitting rotation therebetween. The spars 60 of the rotor blades 56 are connected with the stub shafts 302 by pairs of bolts 304 which fit into meshing ears 306 carried by the spars 60 and the stub shafts 302. One of these bolts 304 can be removed, the arm 3l6 disconnected, and the entire blade 56 turned about the other bolt 304 to fold back against the fuselage 30 of the helicopter for placing the same in a hangar, or for storage.

When the stub shafts 302 are rotated on their own axes, the angles of incidence of the blades 56 are changed. Means for rotating the stub shafts are provided in the form of curved horns 3l0 secured to the stub shafts 362. The horns 3 I' are made up of upper and lower stampings welded together'to form a hollow, strong and light structure. The outer ends of the horns are provided with bars 3l2 having universal pivots 314 at their outermost ends. The pivots 3|4 connect to rods 3l6 having universal pivots 3| 8 at their upper ends connecting the rods 3l6 to points between the ends of the rocker arms 252. With such structure, if the rocker arms 252 are moved up or down at either of the pivot points 254 or 256, the rods'3l6 will raise or lower points 3|4 to rock horns 310 and change the angle of incidence of the rotor blades 56. As pointed out above, when the total pitch control rod 220 is moved, the brackets 246 will be moved accordingly upon the extension 244 of the drive shaft 50 and points 254 will be moved accordingly. At this time, the rocker arms 252 will pivot upon the points 256 and the rods 3l6 will act to move the horns 310 and change the pitch of all the rotor blades 56 simultaneously. When the azimuthal control rods 226 and 228 are moved, the control arms 214 will cause the star 266 to be tilted and the rods 200 will be moved up and down cyclically depending upon the tilt of the control mechanism. Thus, the points 256 will move up and down cyclically and the rocker arms 252 will pivot about the points 254 to cyclically move the rods 3l6 up and down to feather the rotor blades 56 cyclically in each revolution.

Referring again to Fig. 11, means to damp the hunting action hereinbefore mentioned are shown most clearly. Dash pots 320 are pivotally connected by their outer casings to arms 322 mounted upon angular extensions 324 secured to the shanks 300 of the blade structure. Thus, as the blades move back and forth, the arms 322 move back and forth a corresponding degree and pull the casing of the dash not 320 in one direction or the other. The dash pots 320 contain pistons 326 having orifices 328 for passing fluid from one side of the piston 326 to the other. Piston rods 330 connect to the pistons 326 and are pivotally connected upon pins 332 mounted in pairs of ears 334 formed as lateral extensions of the flapping links 242. By such structure, as the blades 56 flap up and down in their cycle, the flapping links 242 also flap freely up and down and the dampers 320 are carried with them. If blades move back and forth, such motion will be damped by the dampers just described. Fluid to the dampers is supplied from a tank in the form of a bonnet 336 mounted on top of the brackets 246. A filler plug and air vent 338 is provided in the bonnet. The bonnet communicates through suitable passages with flexible tubes 340 which connect with the dash pots 320 through restricting valves not shown. The restricting valves are arranged to provide a pressure relief function to prevent damage to the rotor structure upon sudden shocks to different blades or other parts of the rotor mechanism.

In Fig. 12, the control means associated with the rotor head 52 for changing the lift of the rotor blades 56 is shown. When the total pitch lever I92 is raised, the lift of the rotor blades 56 will be increased by increasing the angle of incidence of the blades through linkage now to be described. The lever I92 will rotate around the pivot 204 to pull the rod 206 upward and to the left. Such motion of the rod 206 will cause the bell crank 208 to pull the rod 2l0 toward the left. The rod 2l0 will rotate the bell crank H2 in a clockwise direction to raise the rods H4. The lever 2|6 will be rotated by the rods 2| 4 around the pivot 2|8 to raise the rod 220 conasmaoe 9 nected to the plate 243 at theuppermost' part of the control mechanism 52. When the plate 248 is raise-d, the rocker arm 252 will rotateabout its point of attachment to the rod 260 which is maintained in a fixed position by the cyclical pitch mechanism to be described hereinafter. Thus, the rod 31! ficonnected at a point'between the ends of the rocker arm 2.52 will be raised; The rod 316 will pull up the horn 3m which will cause the spar fifi carrying the blade 56 to be rotated in a clockwise direction and increase its angle of" incidence. With an increased angle of incidence for the blades %,the lift thereof will be increased and more power will be absorbed by the rotor blades frornthe engine to raise the craft into the air.

When the total pitch lever" I B2 is pushed downwardly; the connecting linkage to the rod 220 will pull the rod 220 downwardly to lower the plate 248. of the rotor head 32 to push the rod 3H5 downwardly and lower the horn sue to rotate the spar 60 ofthe rotor blade 56 in a counterclockwise direction anddecrease the pitch thereof.

In: Fig. 13, the cyclical pitch mechanism is shown. The joy stick 59 5 may be movedin any direction in azimuth. For forwardcomponents of movement, the joy stick lfl l rotates about a pivot axis I95 to pull a rod 3% toward the left. The rod 348 will rocka lever 342 about a fixed pivot 344 and pulla. rod 3% toward theleft. The rod 346 will pull the lowerarm of a bell crank 348 toward'the leftand rotate the upper arm upwardly to push a rod 359 upwardly. The arm 355 will push the lever 224 upwardly to raise the rod ZZBconnected tothe aft arm Zl't of the cyclic pitch mechanism. With the rodZiZBraised', the tilt of the aft arm 2W1 willbe up at the rear and down at the front. The two sides will remain at a neutralposition and as the star arms 264 are turned by the shaft, they will reach a low point in their revolution as they point forwardly and a high point in their revolution as they point rearwardly. The arms ZSdofthe star will, when. in theforwardposition, pull down the rod 25fl to rock the arm 252 about its innerpivotal connection 254 to the plate 258, theposition of which is controlled by the total pitch control arm I92" and described above. Hence, downward movement of the rod'EEllwill cause the rod 3IG-to move downwardly and rock the horn am downwardlyto rotate the rotor blade 55 in a counterclockwise direction. and decrease the pitch thereof. Inasmuch as the star arm 2541s at its lowest point when the. arm? is pointing forwardly, the rotor blade 58. will have its lowest angle of incidence at a pointzQO degrees beforethe time that its longitudinal axis points forwardly of? the craft (the horn- 31 ll? acts 90 degrees. ahead of 1 the blade position). When the pivot 3H" for the horn 310 lSjlI'l the rearmostrposition, the axis of :the bladewill; be to the left of the craft and at its highest angle of incidence. By such an arrangement. whenlthe craft is flying forward, becauseof a forward.- control movement. of thejoy stick I294, the b1ade 56 advancing intothawind has the smallest angle of incidence and: theblade retreating: with the wind. will have the highest angle of 1 incidence so thatthe tiprpath plane of. thBzIOtOI'; mechanisin.willbeinclined upwardly adjacent the; rearwardpant of. the ship, in-a manner tobedescribed more. fully. hereinaftem. to give. a: forward com-r ponentof lift. to propelthecrafit.

i To: control the right;-and= left-components of movement .of the craft, the. joy stick. L94; is moved to. the right onto the left, .andwill rotatecaroundi pivots 352 to pull a cable 354 in one direction or the other. The cable 354 leads over suitable pulleys to thearcuate segment 222 for raising and lowering the control rod'228. As lillBjOY stick I94 is moved toward the left; rod 228 is pulled downwardly to lower the control arm 214* which is disposed Ontl lE left handside of therotor head mechanism 52. By lowering theleft handside of thepath of rotation of the star arms 264, the lowest angle ofiincidence of therotorblade 56 will occur when the rotor blade 56" is 'at its forward position in alignment with the longitudinal axis of thecraft because of theQO degree displacement of thehorn control point 314 with: the longitudinal axis of the blade 56. The-highest angle of incidence will: occur when the rotor blade 56- is overthe empennagexportion of the helicopter and hence. the tip? path. plane of the rotor will be inclined. upwardly on thexright21hand side of the helicopter andrdownwardlyi at theleft handlside, to give a horizontal: component of the lift directed toward the left..

The above descriptionnofcontrol effectedlby the joy stick. lfl l has been; only of forward and backward and rightand left movements. It willbe understood, however, that a: helicopter-is capable of; flightin any direction. in. azimuth. with respect tothe body of the helicopter. In order; to effect operation in: any desired direction, the: operator needaonly to-move'the joystick [9d in'the direction invwhich he wishes to. go, and the tip path plane of the rotor. blades will tilt so as. to provide a. horizontal. component of liftin that direction. To obtain moreior. less lift from the rotor blades 56, the pilot changes. the. positionof the total pitch. rod I921, shown in Fig. 12, which opens the throttle so that more power from the engine is suppliedto the. rotor. blades 53. and the angle of incidencecf the blades is changedsimultaneously to increase. the lift. The above operations will be described. more, fullyhereinafter in connection with the practicaloperation of the mechanism.

In Fig. 14, the construction of the tail rotor and the controls therefor. is shown partly indetailand partly diagrammatically. Figs. 15 and 16 are detail views of the drive shaft support and aligning mechanism; In Fig.14, the torque compensation rotor 33 issupported upon a housing 356which contains ashaft' turning hub 358 tow'hich the blades of the tail rotor, 33 are hinged. The drive shaft within the housing 355 has a hole passing longitudinally therethrough through which a control rod 365i may be moved back and forth by a worm, not shown, turned by a wheel 352 operatedbythe ca-ble 2&8; The details of construc tion of this mechanism will not be describedbecause they can be ofsubstantially the same formas that shown in Figs; 5 and 9 of Patent No 2,318,259 mentioned hereihbefore, except that a worm is usedto provide longitudinal movement of" the controlrod 360. The cable 208 is moved back andforth to change the angle of incidence of therotor blades of the rotor 33 by the movement of pedals I95 located in the cockpit; As the pedals IQBlare pushed downwardly, rods 364 rotateibelli' cranks 366: about fixed pivots 368i The bell cranks: are connected by a rod 310 so that each oil the pairs of pedals 1 move simultaneously. Therod 310 rotates an arcuate: segment 312 formed as an extensionof one of the bell cranks 36.6 to move the cable to theright or to the left;

Thus, as a: left; pedal is pushed downwardly; the

cablellilllismoved in adirection so thatlthe rod 360" of the tail rotor assembly moves outwardly to increase: the: pitch of% the blades of. the tail rotor to; pull. theaempennage: sectionaof the: hell 1 1 ward velocity will be at a rate determined by the difference in the power input to the rotor above or below that power required to sustain the craft, or 833 pounds per blade.

In Fig. 18, the attitude of several parts of the craft is shown when the tip path plane of the rotor blades 56 is being tilted forwardly to cause the craft thereafter to move in the forward direction. The operator will move the cyclic pitch control rod I94 forwardly. The star 266 (Fig. will be tilted forwardly an amount in proportion to the tilt of the control rod I94 but not necessarily to the same extent. Upon tilting the star 266, the pitch of he blades 56 will be changed cyclically to cause the tip path plane of the rotor blades lit to be tilted forwardly, and the blades 56 will rotate about a virtual axis of rotation, not in registry with the real axis of rotation containing the drive shaft. The universal blade mounts permit such action without stressing the blades 56 excessively. The tilting of the rotor mechanism, and the forces causing the same will be more fully described in connection with Fig. 23.

In Fig. 19, the action of the helicopter upon being accelerated is shown. The tip path plane of the rotor blades '56 is tilted forwardly from the vertical line and therefore will exert a horizontal component of force and cause the rotor system to be moved substantially horizontally through the air. Because of the inertia of the body of I the helicopter, the body will tilt forward much as a pendulum relative to an accelerated point of suspension. The amount of tilt is limited because of the connections of the flapping links to the rotor blades disposed on opposite sides of the rotor shaft (see Fig. 11). As the helicopter moves forwardly, there will also be a force present to cause it to move upwardly because the power required to sustain the craft will decrease as the speed of the craft increases. ent because when the helicopter is in forward motion there is an additional flow of air through the rotor due to this motion. It is a generally accepted fact that it takes less power to give a large mass of air a small increment of velocity than to give a small mass of air a large increment of velocity. Thus, as the rotor is tilted and moves with respect to the relative wind, a larger mass of air passes through it. Up to speeds of 4'0 to miles per hour, before the drag of the rotor and fuselage have serious effect, the power required will be substantially reduced over that power required for sustaining the craft at zero air speed. Beyond this speed, however, the power required will again increase due to the predominating influence of rotor and fuselage drag.

Due to the forward tilt of the body 30 of the helicopter, the tilt mechanism including star plate 266 will be tilted forwardly with respect to the tip path plane of the rotor blades 56. This tiltin of the mechanism will be a function of the tilt of the body 30 around the point of support of the rotor blades 55. The rate of change of the tilting of the body is very important in the present invention because, within limits, it provides a definite time element for the pilot to react.

, When the body 30 of the helicopter tilts into the position shown in Fig. 19, the cyclic pitch control rod I94 can be moved toward its original position with respect to the fuselage. It will be noted, however, that in this position with respect to the fuselage, the stick is still tilted with respect to a line normal to the flight path. When enough altitude is attained in the climb condition, the

total pitch is reduced by control rod I92 which This force is presis moved from the full-line position shown to a. position in which the pitch and power available to the rotor blades 56 equals that required for level flight.

In Fig. 20, an exaggerated condition of the attitude of the helicopter in level flight has been shown. In this condition, the direction of motion of the entire craft is directly forward. The drag of the relative wind upon the fuselage and surrounding structure will cause the center of gravity of the craft to be swung backwardly with respect to the point of support at the center of the rotor. The tiltin mechanism star plate 266 may be substantially parallel to the longitudinal axis of the body of the helicopter but is tilted with respect to the horizon. Under such conditions, the rotor blades 56 will exert a horizontal component of thrust in the same direction as the flight of the helicopter and this force will be opposed by the drag acting upon the body of the helicopter and the horizontal component of rotor drag. The balances of forces is more clearly illustrated in the diagram Fig. 20a. The thrust will draw the craft forward increasing the drag of the rotor and the drag of the fuselage until their sums equal the propulsive thrust vector. The tilt will always be such that the moment around the center of gravity of the fuselage and the couples of lift-weight and thrust-drag will equalize. The different actions will be described more fully in connection with Fig. 25.

In Fig. 21, the attitude of the helicopter upon decelerating is shown diagrammatically and exaggerated somewhat for clarity. The control rod l 94 is moved rearwardly to cause the tilt mechanism to tilt rearwardly with respect to the body of the helicopter and in some cases of decelerated flight with respect to a line that is normal to the horizon. The action of the tilt mechanism will be to cause the tip path plane of the blades to be opposite to that discussed in connection with Fig. 18 and a rearwardly directed component of thrust will be exerted by the rotor blades to cause the helicopter to decelerate. When decelerating from speed of minimum power to substantially zero air speed, the total pitch rod I92 will be moved from the full-line position shown up to the dotted-line position to increase the total pitch of and power available to the blades as to maintain the helicopter at a given altitude. The reason for increasing the pitch is because when the helicopter slows down with respect to the supporting air, the power necessary to sustain the craft will be increased for the same reasons as pointed out in connection with Fig. 19 when the craft is accelerated except that the action of the controls will be reversed.

From the foregoing, the broad principles of operation of a helicopter will be clear, and the reasons attendant the fact that the helicopter can lift a greater load when taking off in a relatively high wind are also made clear, since relative wind and not absolute motion determines the lift. The details of functioning of different parts described above will be set out below in connection with charts which illustrate these principles. Fig. 22 is a chart having as a base the degrees from zero to 360 of rotation of the rotor blades 56 with respect to the body 30 of the helicopter. Thus, at zero degrees, the rotor blade 56 is directed toward the tail rotor 33. At degrees, in the direction of rotation, the rotor 56 is at the right of the body 30 of the helicopter. At degrees, the rotor 56 is forward of the body of the helicopter. At .270 degrees, the rotor blade 

